The theme of investigations in the PI's laboratory has been that the mechanisms regulating programmed cell death (PCD) in dopamine neurons during development may be relevant to the processes underlying the degeneration of these neurons in neurologic diseases, particularly Parkinson's disease (PD). This approach is based on their demonstration of apoptotic cell death in dopamine neurons during development. They have shown that this natural cell death event is regulated by target interactions; early axon- sparing injury to the target striatum induces death. The PI has shown that death is also induced by disruption of target interaction due to destruction of dopamine terminals with the neurotoxin 6-hydroxydopamine. This was the first demonstration of apoptosis in a living model of Parkinsonism. These studies raise two broad questions which the PI shall address in this proposal. First, what are the molecular mechanisms underlying PCD in dopamine neuron? Second, what are the target-derived factors regulating natural cell death; is glial cell line-derived neurotrophic factor (GDNF) such a factor? The first question will be addressed in the first two Specific Aims. For Aim 1, the PI has considerable preliminary data to indicate that there is induction of synuclein mRNA in his model of induced apoptotic death in dopamine neurons. This gene is of particular interest because it is a candidate gene for familial PD. The PI will examine its protein expression, its developmental expression, and its relationship to other molecules involved in PCD. In the second Aim, the PI will examine the expression of molecules which have been implicated in the initiation or execution of apoptosis. He will focus on c-fos c-jun, the caspases (ICE, CPP32 and r1CH1), and cyclin-dependent kinase 5. The third Aim will extend his prior studies of natural cell death in dopamine neurons, and it will pursue his preliminary data showing that passive immunization to endogenous GDNF augments natural cell death. The significance of these studies is that they will give us new knowledge on the regulation of the viability of dopamine neurons, and will have direct implications for new therapies directed towards the pathogenesis of PD, rather than just its symptoms.